1. Field of the Invention
The present invention relates to an apparatus with ring shape sleeves, and is provided to improve all disadvantages that induced by the draft angle effect. Obviously, the invention is especially adaptable for high precision apparatus such as objective lens holder of optical pick-up head.
2. Description of the Prior Art
Apparatus which is attached to a shaft and moves about a shaft is widespread applied in modern industry. Such application comprises lens holder of rotating type actuator and emery wheel. Obviously, the tolerance between the shaft and other part of the apparatus is an important factor of quality of the apparatus. Generally, the less the tolerance is, the more controllable the apparatus is. No matter how, even the required tolerance is small, the determination of the real region of gap between shaft and apparatus is strongly dependent on how the apparatus is attached to the shaft.
Obviously, it is necessary to form a hole on the apparatus to attach the apparatus and the shaft. Conventional methods to form the hole comprise injection molding and lathe tuning. No matter how, owing to these restrictions of fabrication such as module and cutter should be removed from formed apparatus when the hole is formed, the width of the hole is not uniform. Referring to FIG. 1, when hole 10 is formed in apparatus 12 and module/cutter 14 is moved away, it is obvious that top width W+2xcex4 must be larger than bottom width W or the remove of module/cutter 14 will damage boundary of hole 10. Specifically, there is a draft angle xcex8, and the variance of tolerance 2 xcex4 is proportional to thickness of apparatus 12. Particularly, the draft angle effect is serious when thickness of apparatus 12 is large, and is more serious when aspect ratio of hole 10 is lager for the ratio 2 xcex4/W is not negligible in the case.
It is crystal-clear that when the draft angle effect is not negligible, the real region of gap between the shaft and apparatus is increased and apparatus can not rigorously reattached to the shaft. FIG. 1B shows the condition in that when shaft 16 penetrates hole 10, there is non-uniform gap 18 between shaft 16 and apparatus 12. Therefore, during operation of the apparatus, some disadvantage that induced by the draft angle effect such as lean of apparatus and degraded dynamical characteristics of apparatus will occur. When required accuracy of apparatus is not rigorous, these disadvantages maybe negligible. However, when the apparatus requires rigorous accuracy, such as objective lens holder of optical pick-up head, it is necessary to overcome all disadvantages that induced by the draft angle effect.
According to previous discussion, obviously in fabrication of apparatus that is attached to and move about a shaft, it is important to overcome disadvantages that induced by the draft angle effect. In addition, it is more desired for apparatus that requires rigorous accuracy such as objective lens holder of optical pick-up head.
The main object of the invention is to propose a method that rigorously attaches an apparatus to a shaft.
Another object of the invention is to decrease the tolerance and decrease difficulty of fabrication of the apparatus.
Another object of the invention comprises efficiently improves disadvantages that induced by the draft angle effect.
An incidental object of the invention is to eliminate any dust that appears in the gap between the apparatus and the shaft.
A further object of the invention is to increase interchangeable ability of component parts.
A specific object of the invention is to improve quality of objective lens holder of rotating type actuator.
Another specific object of the invention is to simplify the fabrication and the development of rotating type actuator.
In order to accomplish previous objects, apparatus with ring shape sleeves is proposed. One of the features of the proposed invention is that apparatus and shaft are attached by ring shape sleeves that thickness of any ring shape sleeve is thin enough such that the draft angle effect is negligible. Moreover, ring shape sleeves can be either inlayed in the apparatus or be molded integrally with the apparatus.
Therefore, not only shaft is rigorously attached to the apparatus but also the space between shaft and apparatus is significant decreased. In other words, draft angle effect is efficiently protected. By the way, the apparatus is more controllable and yield of the apparatus is improved. Beside, because the contact area between shaft and apparatus is small, any dust that appears between the apparatus and the shaft is eliminated.